​Social scientists have long known that health disparities are organized in part by the neighborhoods in which we live. Neighborhoods have been found to correlate with rates of asthma, diabetes, heart disease, stroke, functional limitations, and overall mortality, with residents of low-socioeconomic status neighborhoods experiencing higher rates of these ailments in comparison to individuals from more affluent neighborhoods.[1] While there are many mechanisms through which these disparities develop, the physical aspects of neighborhoods on individuals’ microbiota is one potentially significant factor contributing to health outcomes and resulting health disparities.

Photo by Loren Kerns

The term microbiota refers to the trillions of small bacterial cells that live in and on our body, including in our gut. The microbiome refers to all of these bacteria’s genes. Since the National Institute of Health’s launch of the Human Microbiome Project (HMB) in 2007, research on the microbiome and its influence on human health has increased exponentially. Many researchers have found that an individual’s microbiome can play a significant role in determining certain health outcomes.[2]

There are many lifestyle and environmental factors that affect our microbiota composition, and aspects of our neighborhoods have a lot to do with those factors. Researchers have found, for example, that changes in diet rapidly alter our microbiome.[3] Diet, of course, depends on what food is available in one’s community, so someone living in an area with access to only processed foods will have a different microbial composition than someone who lives right next to a healthy food store. It is important to note that many of the factors shown to reduce gut microbial diversity, such as highly processed foods, physical inactivity, stress, heavy antibiotic use, and exposure to pollutants, are disproportionately prevalent in low socio-economic (SES) neighborhoods. A 2016 study, for example, found that as neighborhood socioeconomic-status increases, so does the diversity of the colonic and fecal microbiota.[1] There is even evidence that the presence or absence of green space affects the bacteria to which we are exposed.[4]

This map depicts food deserts in the United States by counties as reported by the USDA in 2010. By: Bldavis2

As our environment and lifestyle affect the composition of our microbiota, our microbiota can in turn influence the onset, progression, and outcomes of disease. Studies have shown that many chronic diseases are characterized by changes in the composition of the intestinal microbiota, and that gut microbiota “play a key role in food digestion and energy harvest, and in the process generate short-chain fatty acids and other metabolic products that regulate fat accumulation, insulin sensitivity, and inflammation.”[1] Researchers have also found that decreased microbial diversity in the gut is more common in individuals with obesity, diabetes, heart disease, and asthma.[1] The bacterial composition of the gut is important for postnatal development and maturation of certain systems that influence the development of the central nervous system.[5] Further, there is evidence that alterations in the composition of the gut microbiota throughout the lifespan may impact the progression and characteristics of certain mental health disorders.[6]

While the mechanisms through which microbiota composition can affect health are still unclear, existing research tells us that there is reason to suspect some sort of causal relationship between microbial composition and the onset and progression of certain diseases.[1] Future research will need to evaluate this relationship and seek to further identify both the pathways that allow our microbiome to impact our health, and the environmental factors that may contribute to socioeconomic and neighborhood differences in microbial composition.

Even if a causal relationship does exist, however, some would argue that the question of “cause or consequence” is not necessarily of the greatest importance. One researcher points out that while we often ask whether changes in the gut microbiome are a cause or a consequence of disease, “a better question may be whether the altered microbiome contributes to the disease.”[7] He goes on to suggest that “whatever the trajectory that leads to the alteration of the neglected microbial organ of our body, it needs to be treated to the best of our abilities, in order to improve the patients’ health.”[7]

This last sentiment reflects the fundamental aim of public health—ultimately, the goal of research is to improve peoples’ lives, and future research should focus on the development and assessment of possible interventions. In order to close persistent health gaps, researchers should further investigate the mechanisms by which health disparities occur in neighborhoods.